A study in the journal Cell sheds new light on the evolution of neurons, focusing on the placozoans, a millimeter-sized marine animal. Researchers at the Center for Genomic Regulation in Barcelona find evidence that specialized secretory cells found in these unique and ancient creatures may have given rise to neurons in more complex animals.
Placozoans are tiny animals, around the size of a large grain of sand, which graze on algae and microbes living on the surface of rocks and other substrates found in shallow, warm seas. The blob-like and pancake-shaped creatures are so simple that they live without any body parts or organs.
These animals, thought to have first appeared on Earth around 800 million years ago, are one of the five main lineages of animals alongside Ctenophora (comb jellies), Porifera (sponges), Cnidaria (corals, sea anemones and jellyfish) and Bilateria (all other animals).
The sea creatures coordinate their behavior thanks to peptidergic cells, special types of cells that release small peptides which can direct the animal’s movement or feeding. Driven by the intrigue of the origin of these cells, the authors of the study employed an array of molecular techniques and computational models to understand how placozoan cell types evolved and piece together how our ancient ancestors might have looked and functioned.
The researchers first made a map of all the different placozoan cell types, annotating their characteristics across four different species. Each cell type has a specialized role which comes from certain sets of genes. The maps or “cell atlases” allowed researchers to chart clusters or “modules” of these genes. They then created a map of the regulatory regions in DNA that control these gene modules, revealing a clear picture about what each cell does and how they work together. Finally, they carried out cross-species comparisons to reconstruct how the cell types evolved.
Time-lapse video of a Trichoplax sp. H2 specimen observed under the microscope. Credit: Sebastian R. Najle/Centro de Regulación Genómica
2023-09-19 13:24:03
Original from phys.org rnrn